A variable speed pumped-storage power generating system employs a secondary excitation device which generates a revolving field by supplying a rotator with a three-phase AC to control a rotation speed of a generator motor.
The secondary excitation device performs PWM control to superimpose, on a carrier, the signal wave desired to be generated, and performs switching between semiconductor elements at intersection points of the carrier and the signal wave to generate a target voltage.
Harmonic components of the carrier frequency used in the PWM control inevitably cause a voltage distortion factor on the primary side of the generator motor. A technique of detecting a voltage distortion factor and controlling a carrier frequency to reduce a voltage distortion factor caused by harmonic components of the carrier frequency has been known.
In contrast, in a variable speed pumped-storage power generating system, harmonics generated on the primary side of a generator motor increase as the impedance frequency characteristic of the electric power system changes. More specifically, when an antiresonance is caused between a harmonic peak frequency which flows out of the generator motor and an impedance of the electric power system viewed from the generator motor, a problem arises in which the harmonic voltage distortion factor of the electric power system increases.
Under the circumstances, it is desired to provide a control device, control method of a secondary excitation device, and a variable speed pumped-storage power generating system, capable of reducing the harmonic voltage distortion factor of an electric power system and a variable speed pumped-storage power generating system.